1. Field of Invention
The present invention relates to a sheet media processing device that images the front and back sides of sheet media such as checks while conveying the sheet media one at a time through a transportation path.
More particularly, the invention relates to a sheet media image reading method that uses a front image sensor and a back image sensor disposed at offset positions along the transportation path to capture front-side image data containing image information on the front of the sheet medium and back-side image data containing image information on the back of the sheet medium, and then accurately extracts the front and back image information from the front-side image data and back-side image data. The invention also relates to a sheet media processing device and sheet media processing system that use this method.
2. Description of Related Art
Check processing devices for processing checks and similar instruments (collectively referred to below as simply checks) are one type of sheet media processing device that images the front and back sides of sheet media. In retail stores as well as banks and other financial institutions, received checks are loaded into a check processing device to read the printed magnetic ink characters and image the front and back sides for transaction processing. The electronic image data captured from the front and back sides is processed by the store or financial institution so that it can be used as the equal of the actual check, and the actual check is returned to the person that presented the check (the presenter). A magnetic head, a front image sensor, and a back image sensor in the check processing device read the magnetic ink characters and capture the front and back images while the checks are conveyed one at a time through the transportation path.
If the front image sensor and back image sensor are positioned opposite each other on the opposite sides of the transportation path, part of the light emitted for imaging by the image sensor on one side will stray and affect imaging by the other image sensor. If contact image sensors are used, a pressure roller for pressing the conveyed check to the image sensor surface must be disposed opposite each image sensor on the other side of the transportation path. As a result, Japanese Unexamined Patent Appl. Pub. JP-A-2007-137035 teaches a check processing device that has the front image sensor and back image sensor disposed on opposite sides of the transportation path at positions offset (shifted) from each other in the transportation direction.
Because the image sensors read images of the checks as the checks pass by, the image sensors may not be able to accurately image the leading end or trailing end parts of the check, and some of the check image data may be lost. This can be avoided by starting the imaging operation before the check reaches the reading position of each image sensor, and continuing to read until after the trailing end has passed the reading position. More specifically, if the reading operation continues from positions beyond the leading end and trailing end of the check, image data for the entire check can always be captured. Because the entire check is thus included, image data that contains a margin at the leading end and the trailing end of the check is acquired from each image sensor. This margin is read from parts of the transportation path where the check is not present, and the image in this margin is darker than the images captured from the check. The margin can then be removed by extracting the portion of the captured image data where the brightness is greater than or equal to a predetermined level, and images of only the front and back sides of the check can thus be acquired.
However, checks are also printed with a wide variety of background designs on the surface. Some designs include a dark colored border or decoration at the leading end and trailing end of the check. If an image processing operation that extracts the surface image data of the check based on the image brightness is applied to the image data acquired from the front of such checks, the border around the front of the check may be incorrectly determined to be part of the margin instead of part of the desired check image, resulting in only the image inside the border being extracted as the front-side image data. Note that this type of border or decorative image is not generally printed at the leading and trailing ends on the back side of the check.
In this situation the extracted front image of the check is smaller than the back image by the size of the border or decoration that is identified as part of the margin. If the front image and back image are different sizes, the images are not considered to be authentic images of the front and back of the check, and the resulting images cannot be used as legal equivalents of the actual check. In order to accurately extract the front image of the check, the size of the front image can be referenced to the size of the back image of the check where the background design is not printed. The front image of the entire check including the border can be extracted from the front-side image data based on the coordinates of the back image acquired by writing the back image to memory.
As described above, the front image sensor and the back image sensor are disposed at offset positions in the transportation direction. Information about these known, fixed offset positions can be stored in the check processing device. However, if there is any deviation in the distance between the front image sensor and the back image sensor and the front image information contained in the front-side image data is extracted based on the coordinates of the back image information contained in the back-side image data, the position of the extracted image will be shifted by an amount equal to the deviation in the sensor-to-sensor distance. As a result, the extracted front image will be cut off at one end and contain part of the margin at the other end. The resulting front image information is thus deficient, and cannot be used as the equal of the actual check.